Velocity and reflection structure of the Sudbury Structure from laboratory measurements

Compressional wave velocities and densities have been measured to hydrostatic confining pressures of 600 MPa for 120 drill core samples representing all major lithologies exposed in the Sudbury Structure (SS) in order to constrain petrologic interpretations of seismic reflection, refraction and logging data obtained along the Sudbury Lithoprobe Transect. A composite acoustic impedance section, constructed for the centre of the structure by stacking the drilled sections on the basis of petrology, shows that the Chelmsford greywacke/Onwatin shale and shale/Onaping tuff contacts near the top of the section should be strong reflectors, the Granophyre/Norite contact should be a moderate reflector and the tuff/Granophyre contact will not reflect seismic energy at all. The Norite/Levack gneiss contact at the base of the section will be a strong reflector locally. These results are in excellent agreement with Lithoprobe seismic reflection results and provide a means for interpreting the reflection data in terms of petrology across most of the structure. Since both of the major types of ore bodies found in the SS are coincident with reflective contacts, seismic reflection profiling should be a valuable tool for base metal exploration in the region.